Saint-Sulpice is the second largest church in Paris, following Notre-Dame. Gittard moved to Paris, buying an architect's commission in the Bâtiments du Roi as early as 1655; throughout his life he was to engage in building- and property-speculation in the parish of St Sulpice as did Louis and François Le Vau on the Ile Saint-Louis. His plans for the huge new church of St Sulpice were preferred to those of Louis Le Vau: Gittard supplied the general design and built the sanctuary, ambulatory, apsidal chapels, transept and north portal (1670-1678), after which work was suspended for lack of funds. The nave and side-chapels were built in 1719-1745 by Gilles-Marie Oppenord and Giovanni Servandoni, to Gittard's designs.